30 ANIMAL MECHANICS 



those which navigate the gulf of Finland. Their 

 masts are not attached at all to the hull of the 

 ship, but simply rest upon the step. 



Although the spine has not a strict resem- 

 blance to the mast, the contrivances of the ship- 

 builder, however different from the provisions of 

 nature, show what object is to be attained ; and 

 when we are thus made aware of what is necessary 

 to the security of a column on a movable base, we 

 are prepared to appreciate the superior provisions 

 of nature for giving security to the human spine. 



The human spine rests on what is called the 

 pelvis, or basin ; a circle of bones, of which the 

 haunches are the extreme lateral parts ; and the 

 sacrum (which is as the keystone of the arch) may 

 be felt at the lower part of the back. To this 

 central bone of the arch of the pelvis the spine is 

 connected ; and, taking the similitude of the mast, 

 the sacrum is as the step on which the base of 

 the pillar, like the heel of the mast, is socketed 

 or mortised. The spine is tied to the lateral parts 

 of the pelvis by powerful ligaments, which may 

 be compared to the shrouds. They secure the 

 lower part of the spine against the shock of lat- 

 eral motion or rolling ; but, instead of the stays 

 to limit the play of the spine forwards and back- 

 wards in pitching, or to adjust the rake of the 

 mast, there is a very beautiful contrivance in the 

 lower part of the column. 



